1. Field of Invention
The present invention relates to a new family of potassium channels. More specifically, the invention relates to the cloning of new human potassium channels that constitute the members of a new functional and structural group of potassium channels. The abundance of these channels and their presence in a large number of tissues are such as to confer on them a fundamental role in the transport of potassium in a large number of types of cells. The properties of the channels suggest highly interesting applications in the physiology of mammals, especially humans.
2. Description of the Related Art
Potassium channels are ubiquitous membrane proteins that form the largest family of ion channels both in term of functions and structures. By determining and modulating the membrane potential, they play a major role in neuronal integration, muscular excitability as well as hormone secretion (Rudy, 1988; Hille, 1992). More than 40 genes encoding K.sup.+ channel subunits are now identified in mammals. These subunits fall into two structural classes of pore-forming subunits (Shaker and IRK) (Pongs, 1992; Jan and Jan, 1994; Doupnik et al., 1995; Fakler and Ruppersberg, 1996; Kohler et al., 1996) and four structural classes of auxiliary subunits (Kv.beta., Kca.beta., SUR and IsK) (Takumi et al., 1988; Knaus et al., 1994; Pongs, 1995; Inagaki et al., 1996). All Shaker-type subunits have a conserved hydrophobic core containing 6 transmembrane segments (TMS). Associations of Shaker-type subunits with accessory subunits such as Kv.beta., Kca.beta. or IsK give rise to voltage-dependent K.sup.+ channels (Pongs, 1995; Barhanin et al., 1996; Fink et al., 1996a; Sanguinetti et al., 1996) and Ca.sup.2+ -dependent K.sup.+ channels (MacCobb et al., 1995; MacManus et al., 1995). Subunits of inward rectifier K.sup.+ channels (IRK) have only two TMS (Doupnik et al., 1995; Lesage et al., 1995; Fakler and Ruppersberg, 1996). Some IRKs give rise to ATP-sensitive K.sup.+ channels when they are associated with sulfonylurea receptors (SUR) subunits (Inagaki et al., 1996). Despite a very low overall sequence similarity, Shaker and IRK pore-forming subunits share a conserved domain called the P domain. This peculiar motif is an essential element of the K.sup.+ -selective filter of the aqueous pore and is considered as the signature of K.sup.+ channel-forming proteins (Heginbotham et al., 1994).
In the above-identified parent patent application, there is described a new family of mammalian K.sup.+ channel subunits. Despite a low sequence similarity between them (less than 28% of amino acid identity), both cloned members of that family (TWIK-1 and TREK-1) possess the same overall structure with four TMS and two P domains (Fink et al., 1996b; Lesage et al., 1996a; Lesage et al., 1997). The conservation of this structure is not associated with a conservation of the functional properties: TWIK-1 gives rise to weakly inward rectifier K.sup.+ currents (Lesage et al., 1996a) while TREK-1 produces outward rectifier K.sup.+ currents (Fink et al., 1996b). However, both channels are open at the resting potential and are able to drive the resting membrane potential near the K.sup.+ equilibrium potential. This common property suggests that these channels control the resting membrane potential in a large set of cell types.